Rotaviruses are the primary cause of acute dehydrating diarrhea in infants and young children and are responsible for ~600,000 deaths worldwide per year. Their impact on human health has stimulated extensive efforts towards the development of rotavirus vaccines by the Laboratory of Infectious Diseases (LID). Large-scale phase III trials showed that a rhesus rotavirus-based tetravalent vaccine developed by the LID was highly effective in protecting young children against the severe and life-threatening dehydrating diarrhea caused by these viruses. The tetravalent vaccine was approved for use in humans by the FDA, marketed by Wyeth Laboratories as Rotashield, and administered to approximately one million children. However, because of post-marketing concerns that the vaccine may infrequently induce intussusception, the use of the vaccine at the present time has been discontinued. Due to the great impact that rotavirus illness continues to have on human mortality and morbidity, it remains a goal of the Laboratory to develop vaccines against these agents that are effective and safe. The primary goal of this project is the development of a reverse genetics system that can be used to alter the genetic information of the rotavirus genome. Such a system can be used to identify loci within the genome that influence the growth characteristics, antigenic properties, and virulence of rotaviruses. With this knowledge, the system can be used to create a new generation of vaccines by the introduction of attenuating mutations into the genome of virulent isolates of human rotaviruses. Secondary goals of this project include (i) identification of viral gene products that interfere with innate cellular immune responses, and thereby affect the virulence of the virus, and (ii) analysis of the impact that host cell lines have on the protein coding capacity of vaccine strains of rotavirus. In the past year, we have determined a complete and accurate sequence of the genome of the SA11 prototype strain of rotavirus, and created a corresponding set of cDNAs to the SA11 genome segments. These cDNAs are being used in an attempt to establish a rotavirus reverse genetics system. We have also carried out studies that have been successful in further defining the mechanism by which rotavirus subverts the induction of host antiviral responses in infected cells.